Medical leads having forced strain relief loops

ABSTRACT

Strain relief loops are forced by being formed into medical leads such that a body of the lead imposes a force to regain the loop if the loop has been disturbed. Because the strain relief loop is forced, the surgeon implanting the medical lead is not required to create the strain relief loop as a step in the implantation procedure. Forcing the strain relief loop ensures that the strain relief is achieved. The forced strain relief loop also ensures that the loop is present to reduce heating at the electrodes of the medical caused by exposure to excessive radiofrequency energy. The forced strain relief loop may be created by heating the lead body while held in the loop configuration by a mold to cause the loop configuration to persist once the medical lead is removed from the mold.

TECHNICAL FIELD

Embodiments are related to medical leads that carry electrical signalsfrom a medical device. More particularly, embodiments are related tomedical leads with forced strain relief loops.

BACKGROUND

Medical leads provide electrical stimulation from a medical device to atarget site within a body of a patient. The medical device is typicallyimplanted or otherwise installed on the body in an accessible area atsome distance from the target site, and the medical lead is routed tothe target site either through a percutaneous procedure or by surgicalimplantation depending upon the type and size of the medical lead beingimplanted.

Because the medical lead extends some distance between the medicaldevice and the target site within the body, the medical lead is subjectto forces imposed by movements of the patient. In particular, themedical lead may be subjected to strain. To address the strain, themedical lead may be routed by creating a loop that relieves the strainby the loop making available an additional length of the lead.

An additional benefit of the strain relief loop occurs in relation toradiofrequency (RF) heating at the electrodes. RF heating can occur whenthe patient is exposed to relatively high levels of RE energy such asduring a magnetic resonance imaging (MRI) scan. The metal conductorswithin the lead such as filars connected to the electrodes have currentinduced by the RF energy. This induced current can produce heatingwithin the medical lead and at the electrodes. The presence of thestrain relief loop, particularly if the loop is created in relativelyclose proximity to the distal end of the medical lead where theelectrodes are located, reduces such heating which improves the comfortof the patient and lessens the risk of injury during MRI scans.

An issue is that strain relief loops may be considered optional and/ormay be overlooked by some clinicians and therefore are not necessarilycreated in all instances. Thus, one implantation of a given medicalsystem that includes a strain relief loop may offer better protectionfor the patient from RE' heating than a same medical system that isimplanted in a patient without a strain relief loop.

SUMMARY

Embodiments address issues such as these and others by providing medicalleads and related systems where the medical lead has a forced strainrelief loop. The strain relief loop is forced by having the strainrelief loop be formed by a lead body of the medical lead in such a waythat the lead body applies force to regain the formed loop whenever theformed loop is disturbed. In this manner, forming the strain relief loopis not a step of the implantation process and therefore is not optionalconsidering the medical lead already has the forced strain relief loopat the time of implantation.

Embodiments provide a medical lead that includes an insulative lead bodyhaving a formed loop such that the insulative lead body imposes a forceto regain the formed loop when the formed loop is disturbed. The medicallead further includes at least one electrical conductor surrounded bythe insulative lead body and at least one electrical contact on aproximal end of the lead body, the at least one electrical contact beingelectrically coupled to the at least one electrical conductor. Themedical lead further includes at least one electrode on a distal end ofthe lead body, the at least one electrode being electrically coupled tothe at least one electrical conductor.

Embodiments provide a medical system that includes a medical device witha stimulation output connector and a medical lead. The medical leadincludes an insulative lead body having a formed loop such that theinsulative lead body imposes a force to regain the formed loop when theformed loop is disturbed. The medical lead further includes at least oneelectrical conductor surrounded by the insulative lead body and at leastone electrical contact on a proximal end of the lead body, the at leastone electrical contact being electrically coupled to the at least oneelectrical conductor and in electrical contact with the stimulationoutput connector. The medical lead additionally includes at least oneelectrode on a distal end of the lead body, the at least one electrodebeing electrically coupled to the at least one electrical conductor.

Embodiments provide a method of making a medical lead that involvessurrounding a conductor with an insulative lead body and mounting acontact on a proximal end of the insulative lead body and in electricalconnection to the conductor. The method further involves mounting anelectrode on a distal end of the insulative lead body and in electricalconnection to the conductor. Additionally, the method involves forming aloop in the insulative lead body such that the insulative lead bodyimposes a force to regain the formed loop when the formed loop isdisturbed.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a medical system environment where a forcedstrain relief loop is present on a medical lead.

FIG. 2 shows a process for creating an example of a medical lead havinga forced strain relief loop.

FIG. 3 shows two mold halves that form the strain relief loop onto themedical lead,

FIG. 4A shows a first view of an example of the forced strain reliefloop according to various embodiments of a medical lead.

FIG. 4B shows a second view of an example of the forced strain reliefloop according to various embodiments of a medical lead.

FIG. 5 shows another example of the forced strain relief loop accordingto various embodiments of a medical lead where a protective band ispresent about two adjacent leads.

DETAILED DESCRIPTION

Embodiments provide forced strain relief loops on medical leads. Thestrain relief loop is formed on the lead body so that the loop isregained whenever disturbed by force imposed by the lead body. Thus, thestrain relief loop is not optional but is present on the medical leadwhen being implanted and is re-established automatically by the actionof the lead body if the loop is manipulated.

FIG. 1 shows an example of a medical system 100 that includes a medicaldevice 102 and a medical lead 104. The medical device 100 producesstimulation signals and the medical lead 104 which is attached to astimulator output of the medical device 100 delivers the stimulationsignals to a set of electrodes 106 on a distal end of the medical lead104. The set of electrodes 106, such as a paddle having a grid ofelectrodes, are positioned at a target stimulation site so that thestimulation signals provide stimulation therapy to the body 112 of thepatient.

The medical lead 104 includes a forced strain relief loop 108. Thisstrain relief loop 108 is already formed on the lead 104 prior toimplantation. Thus, a surgeon implanting the medical lead 104 is notrequired to form the strain relief loop 108 but instead positions themedical lead 104 including the forced loop 108 within the body of thepatient 112. The strain relief loop 108 retains the loop shape duringimplantation and thereafter. Thus, benefits of the strain relief loop108 are ensured, such as the strain relief itself as well as thereduction in RF heating should the patient 112 be exposed to significantRF energy such as during an MRI scan.

It has been found that at typical MRI frequencies, producing the medicallead 104 with the forced strain relief loop 108 at between 5 and 15centimeters from the distal end 106 provides the best level of heatingreduction at the distal end 106 where the electrodes are present. Thedistance of the forced strain relief loop 108 to the distal end may bemeasured from an intersection point 110 where the medical lead 104 haslooped back onto itself which is also referred to as the crossover.

This intersection point 110 tends to develop more heating from RF energythan at other points along the medical lead 104. Therefore, the medicallead 104 may include features to alleviate any issues that might arisefrom the additional heating at the intersection point 110. Thesefeatures may be of various forms. Some examples include an increasedthickness of the lead body at the intersection point 110 and/or aprotective sleeve that covers the intersection point 110. Such examplesare discussed in more detail below with reference to FIGS. 4 and 5.

While FIG. 1 shows a single medical lead 104, some embodiments mayprovide for multiple adjacent medical leads, with each having a loop 108and the loops may be made adjacent. For example, a distal end 106 with apaddle may have many electrodes such that a single paddle is connectedto two adjacent lead bodies. As another example where there are multiplemedical leads 104, each lead 104 may have a separate distal end 106 andthe forced loops 108 of each lead are may be formed adjacently to oneanother.

FIG. 2 shows a process for creating one example of a medical lead 104with a forced strain relief loop 108. In this example, the processbegins with one or more filar conductors 202 which may be coiled filarsas shown or may be cabled filars. Generally, there is a filar conductorpresent for each proximal contact and each distal electrode that will bepresent on the completed medical lead 104. The one or more conductors202 may be constructed of various conductive biocompatible materialssuch as MP35N, MP35N with a silver core, titanium molybdenum, and thelike. Each conductor typically has an insulative coating.

In this particular example, an inner insulative lead body layer 204 isfitted to or otherwise applied to surround the one or more conductors202. The inner insulative lead body layer 204 may surround the conductoreither by forming a lumen that the conductor 202 is present within or byencapsulating the conductor 202. The inner insulative lead body layer204 may be constructed of various non-conductive biocompatible materialssuch as polyurethane, silicone, silicone-polyether-urethane, and thelike. The inner insulative lead body layer 204 may be fitted to theconductors 202 by building the layer 204 separately and then stringingthe conductors 202 through the lumen of the layer 204. Alternativemanners of applying the layer 204 are also applicable, such as forexample extruding or injection molding the layer 204 onto the conductors202.

In some embodiments, the medical lead 104 may now be ready to haveproximal contacts 210 and distal electrodes 216 on a distal paddle 218installed and also have the forced strain relief loop 108 formed in thelead body layer 204. However, in some cases it may be desirable toprovide additional structure such as shielding to further protect themedical lead 104 from unwanted RE heating on the filar conductors 202and electrodes 216.

In one embodiment for providing such additional structure, a next actiontaken is to provide a conductive shield 206 about the inner insulativelead body 204. In the particular example shown, the conductive shield206 is a braided shield that has been placed about the inner insulativelead body 204. The braided shield 206 may be applied in various ways,such as by being braided directly onto the insulative inner lead body204. The braided shield may be constructed from various biocompatibleconductive materials such as tantalum, titanium, and other similarlyconductive materials.

The conductive shield 206 may take other forms as well. One example is afoil tube that wraps about the inner insulative lead body 204. Anotherexample is a metallic layer that has been sputtered onto the outersurface of the insulative inner lead body 204. Utilizing a carbonnanotube structure as a dopant or a coating to the body 204 is yetanother example.

The shield 206 may then be protected by applying an insulative outerleady body 208 that surrounds the shield 206 and hence the insulativeinner lead body 204 and conductors 202. The insulative outer lead body208 may be constructed of various non-conductive biocompatible materialssuch as the same materials listed above for the inner body layer 204.The insulative outer lead body layer 208 may be applied in various ways,such as by fitting the layer 208 onto the shield 206 and layer 204 andutilizing a reflow process, extrusion, or injection molding.

In addition to applying the insulative outer lead body 208, the proximalcontacts 210 and distal paddle 218 and/or distal electrodes 216 areinstalled and electrically connected to the corresponding electricalconductors 202 in the conventional manner. At this point, the medicallead 104 is complete. However, the strain relief loop 108 may then beformed in the insulative lead bodies 204 and/or 208 in such a manner toforce the strain relief loop 108 to persist on the medical lead 104.

One manner of forming the stain relief loop 108 is to utilize a mold 220that includes a looped passageway 222 that the medical lead 104 ispositioned within at the appropriate point along the medical lead 104.Heat is then applied to the mold 22.0 and medical lead 104 within themold 220 to force the strain relief curve to persist in the insulativelead body of the medical lead 104. The medical lead 104 is then removedfrom the mold 220 and is ready to be packaged for shipment with theforced strain relief loop 108 present. For embodiments where multiplelead bodies are looped adjacently, each lead body may be baked inseparate molds and then made adjacent once removed or alternatively, themold 220 may be sized to accommodate multiple adjacent lead bodies andform the loop 108 in the multiple leads 104 simultaneously.

Some specific examples for heating the medical lead 104 to create thestrain relief loop are as follows. In one example, a polyurethane leadbody with a hardness of 80 Shore A, the lead 104 is heated atapproximately 220 to 270 degrees Fahrenheit for approximately 20-30minutes. In another example, a polyurethane lead body with a hardness of55 Shore D, the lead 104 is heated at approximately 230 to 280 degreesFahrenheit for approximately 20-30 minutes.

An example of the mold 220 is shown further in FIG. 3 in the openedstate. Here, the mold 220 has two halves 302, 304. Each half 302, 304may be constructed of a material such as stainless steel, aluminum, andthe like that is capable of holding the lead 104 in the loopedconfiguration while also distributing heat to the medical lead 104. Thehalf 302 includes a looped channel 306 where one direction of the loophas a deeper channel portion 310 at the intersection point to allow themedical lead 104 to cross over itself within the mold 220. Similarly,the half 304 includes a looped channel 308 where one direction of theloop has a deeper channel portion 312 at the intersection point to alsoallow the medical lead 104 to cross over itself within the mold 220.These two halves 302, 304 are brought into engagement with the medicallead 104 present within the channels 306, 308, and then heat is appliedsuch as by placing the mold 220 including the medical lead 104 within anoven.

Other manners of forcing the strain relief loop 108 are also available.These include bonding the two portions of the outer body 208 together atthe intersection point. This bond may be produced in various ways, suchas by using an adhesive or by melting the two portions together. Thebond may later be broken while preserving the loop upon implanting thelead to maintain the strain relief function of the loop.

FIGS. 4A and 4B show an example of a lead 104′ that has a modified leadbody portion 402 present at the intersection point 110. In this example,the modified lead body portion 402 has a greater diameter and hence agreater thickness than the remainder of the medical lead 104′. Thisincreased thickness at the modified portion 402 maintains a greaterseparation between internal conductive items of the medical lead 104′such as filar conductors and/or shields of the intersecting passes ofthe medical lead 104 at the intersection point 110. Such separationreduces the amount of RE heating that is produced by the intersectionpoint 110. This separation is best viewed in the cross-sectional view ofFIG. 4B take at the intersection point, where the shields 206 andconductors 202 of each pass of the lead 104 have increased separationdue to the enlarged lead body portion 402.

Additionally, the increased thickness of the modified portion 402creates a greater separation between the conductive items within themedical lead 104′ at the intersection point 110 and the tissue of thepatient present at the intersection point 110. Thus, the tissue of thepatient is also better insulated from the RF heating by the modifiedportion 402. In FIG. 4B, the modified portion 402 is present on one passof the lead 104. If the same amount of separate of the shield 206 andconductors 202 are desired for both passes, then both passes of the leadshown in FIG. 4B would be provided with the increased thickness as shownfor modified portion 402.

FIG. 5 shows an example of two adjacent medical leads 104, 105 that alsoincludes a sleeve 502 positioned on the medical leads 104, 105 so as tocover the medical leads 104, 105 at the intersection point 110 of both.This sleeve 502 may be installed on the leads 104, 105 prior to formingthe strain relief loops 108 and the sleeve 502 can be formed into theloop configuration as well. Alternatively, the sleeve 502 can be addedafter the loops 108 have been formed. The sleeve 502 may be constructedof materials such as PEEK, polyurethane, silicone, and the like. Thesleeve 502 provides the same benefits as the modified portion 402 ofFIG. 4. The sleeve 502 provides separation of conductive items betweenthe two passes of the lead body 104 at the intersection point 110 toreduce overall RF heating of the intersection point 110. Additionally,the sleeve 502 provides an additional layer of insulation to furtherseparate the conductive items of the medical lead 104 at theintersection point 110 from the tissue of the patient. For embodimentswhere multiple leads 104, 104 are looped adjacently as shown, analternative is for a sleeve 502 to be present on each lead 104, 105individually rather than a single sleeve 502 surrounding the multiplelead bodies. Additionally, a sleeve 502 may be providing around themedical lead 104 for scenarios where only the single medical lead 104 ispresent.

While embodiments have been particularly shown and described, it will beunderstood by those skilled in the art that various other changes in theform and details may be made therein without departing from the spiritand scope of the invention.

What is claimed is:
 1. A medical lead, comprising: an insulative leadbody having a formed loop such that the insulative lead body imposes aforce to regain the formed loop when the formed loop is disturbedwherein the formed loop creates an intersection point of the insulativelead body; at least one electrical conductor surrounded by theinsulative lead body; at least one electrical contact on a proximal endof the lead body, the at least one electrical contact being electricallycoupled to the at least one electrical conductor; and at least oneelectrode on a distal end of the lead body, the at least one electrodebeing electrically coupled to the at least one electrical conductor. 2.The medical lead of claim 1, wherein the insulative lead body has agreater thickness at the intersection point.
 3. The medical lead ofclaim 1, further comprising a sleeve that is positioned over theinsulative body at the intersection point.
 4. The medical lead of claim1, further comprising a conductive shield surrounding the conductor. 5.The medical lead of claim 4, wherein the insulative lead body surroundsthe conductive shield.
 6. The medical lead of claim 5, wherein theinsulative lead body comprises an inner layer and an outer layer,wherein the inner layer surrounds the conductor, wherein the conductiveshield surrounds the inner layer, and wherein the outer layer thatsurrounds the conductive shield.
 7. A medical system, comprising: amedical device with a stimulation output connector; and a medical leadcomprising: an insulative lead body having a formed loop such that theinsulative lead body imposes a force to regain the formed loop when theformed loop is disturbed, wherein the formed loop creates anintersection point of the insulative lead body; at least one electricalconductor surrounded by the insulative lead body; at least oneelectrical contact on a proximal end of the lead body, the at least oneelectrical contact being electrically coupled to the at least oneelectrical conductor and in electrical contact with the stimulationoutput connector; and at least one electrode on a distal end of the leadbody, the at least one electrode being electrically coupled to the atleast one electrical conductor.
 8. The medical system of claim 7,wherein the insulative lead body has a greater thickness at theintersection point.
 9. The medical system of claim 7, further comprisinga sleeve that is positioned over the insulative body at the intersectionpoint.
 10. The medical system of claim 7, further comprising aconductive shield surrounding the conductor.
 11. The medical system ofclaim 10, wherein the insulative lead body surrounds the conductiveshield.
 12. The medical system of claim 11, wherein the insulative leadbody comprises an inner layer and an outer layer, wherein the innerlayer surrounds the conductor, wherein the conductive shield surroundsthe inner layer, and wherein the outer layer that surrounds theconductive shield.
 13. A method of making a medical lead, comprising:surrounding a conductor with an insulative lead body; mounting a contacton a proximal end of the insulative lead body and in electricalconnection to the conductor; mounting an electrode on a distal end ofthe insulative lead body and in electrical connection to the conductor;and forming a loop in the insulative lead body such that the insulativelead body imposes a force to regain the formed loop when the formed loopis disturbed, wherein the formed loop creates an intersection point ofthe insulative lead body.
 14. The method of claim 13, wherein formingthe loop comprises placing the insulative body within a mold that holdsthe insulative body in the loop and heating the insulative body withinthe mold.
 15. The method of claim 13, wherein surrounding the conductorwith an insulative body comprises surrounding the conductor with aninner insulative lead body portion, the method further comprisingsurrounding the inner insulative lead body portion with a conductiveshield, and wherein surrounding the conductor with the insulative bodyfurther comprises surrounding the conductive shield with an outerinsulative body portion.